Method for controlling the air system in an internal combustion engine

ABSTRACT

A method for closed loop controlling the air system in an internal combustion engine, in particular a diesel internal combustion engine with a first actuating element for recirculated exhaust gas in the exhaust gas recirculation tract and a second actuating element for air in the inlet tract, the two actuating elements being adjusted as a function of each other. In order to increase the quality of closed loop control, provision is made for each actuating element to be controlled separately by its own respective controller, each controller being optimally configured for the respective controlled system, and a target value being provided for each controller.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 12/223,077,filed Sep. 22, 2008, now U.S. Pat. No. 8,126,639.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for closed loop control of the airsystem in an internal combustion engine, in particular a diesel internalcombustion engine, with a first actuating element for recirculatedexhaust gas in the exhaust gas recirculation tract and a secondactuating element for air in the inlet tract, the two actuating elementsbeing adjusted as a function of each other, and also to a device forcarrying out the method. Furthermore, the invention relates to a methodfor controlling the characteristic values of combustion in an internalcombustion engine with at least one control path.

2. The Prior Art

U.S. Pat. No. 6,105,559 A discloses an inlet and exhaust gasrecirculation system for an internal combustion engine, the actuators,the exhaust gas recirculation valve and throttle flap being actuated asa function of each other by a single actuating element (actuator). Thetwo A diesel internal combustion engine with an inlet system and anexhaust gas recirculation system is known from U.S. Pat. No. 6,732,723B1, an actuator being arranged in the inlet tract and an actuator in theexhaust gas recirculation tract. The two actuators are connected to theoutput of a single controller. A rigid logic divides the actuatingsignal at the controller output onto the two actuating elements.

The behaviour of the controller used in the prior art for both actuatingelements represents a compromise, as a result of which the controllercan be optimally configured for neither of the two controlled systems.

The invention relates to a method for closed loop controlling the airsystem in an internal combustion engine, in particular a diesel internalcombustion engine, with a first actuating element for recirculatedexhaust gas in the exhaust gas recirculation tract and a secondactuating element for air in the inlet tract, the two actuating elementsbeing adjusted as a function of each other, and also to a device forcarrying out the method. Furthermore, the invention relates to a methodfor controlling the characteristic values of combustion in an internalcombustion engine with at least one control path.

U.S. Pat. No. 6,105,559 A discloses an inlet and exhaust gasrecirculation system for an internal combustion engine, the actuators,the exhaust gas recirculation valve and throttle flap, being actuated asa function of each other by a single actuating element (actuator). Thetwo actuators are joined together by a mechanical coupling. Only oneactuating element and one controller are provided.

A diesel internal combustion engine with an inlet system and an exhaustgas recirculation system is known from U.S. Pat. No. 6,732,723 B1, anactuator being arranged in the inlet tract and an actuator in theexhaust gas recirculation tract. The two actuators are connected to theoutput of a single controller. A rigid logic divides the actuatingsignal at the controller output onto the two actuating elements.

The behaviour of the controller used in the prior art for both actuatingelements represents a compromise, as a result of which the controllercan be optimally configured for neither of the two controlled systems.

A further drawback is that the given structures impose markedrestrictions in the selection of the actuating element boundaries. Thisgives rise to the problem that the controllery bandwidth is small and adifferent division of the actuators for other modes of operation ispossible only to a limited extent.

It is known to control combustion in a stationary manner, i.e. at anoperating point with a specific filling of the cylinders, via at leastone injection parameter, in such a way that the characteristic valuesfor the actual combustion and the desired combustion correspond.Deviations in the filling are compensated for by a controller in the aircontrol path until the actual and the desired filling correspond. Thetarget values for combustion in the stationary mode are datafied overthe course of the calibration process. In this case, the target valuefor a reference variable is defined at an operating point. The targetvalue is considered in conjunction with all other operating states atthis operating point (in particular the filling). The stationary targetvalue for the filling is stored in a memory at the same time as thetarget value for combustion. In this case, the actuators which determinethe filling are set in such a way that the actual filling and thedesired filling are equated. Based on the target value for thecombustion position and the feedback about the actual combustion, theset parameters for combustion are changed in such a way that the actualcombustion approximates the desired combustion. The adjustment variablesare typically injection parameters, such as the moment of injection,injection pressure, quantity injected or the like. These can be adjusted(as a function of the injection system) at least within a combustioncycle. At the transition from one operating point to another, it ispossible for the combustion control means to set the new value for theadjustment variables in a very short time. Nevertheless, the filling ofthe cylinders has based on the fuel control path a very different timeconstant, as a result of which the adjustment values for combustion inthe fuel control path transiently do not match the current filling. Thisleads either to increased emissions with increased combustion noise orto low engine torque while at the same time consuming an increasedquantity of fuel. In the past, these interactions could be reduced onlyat very great expense.

The object of the invention is to avoid these drawbacks and to increaseof the controllery quality during closed loop control of the air system.A further object of the invention is to reduce emissions and alsocombustion noise and at the same time to improve the evolution oftorque.

SUMMARY OF THE INVENTION

According to the invention, this is achieved in that each actuatingelement is controlled separately by a dedicated controller in each case,wherein each controller is optimally configured for the particularcontrolled system, and wherein a target value is provided for eachcontroller. In this case, it is provided that at each moment only one ofthe two controllers is activated and the other controller deactivated,the actuating element, the controller of which is deactivated, beingcontrolled by means of a defined value.

It is crucial that each actuating element has its own independentcontroller. Each controller can thus be optimally configured for itscontrolled system, as a result of which a higher bandwidth and betterlevelling behaviour can be achieved. A program logic switches over inthis case between the two controllers, wherein at each moment only oneof the two controllers is active and the actuating element, thecontroller of which is deactivated, is controlled by means of a definedvalue.

The actuating ranges of the two actuating elements are directly adjacentto each other. In other words, once the actuating range of the firstactuating element (actuator for the exhaust gas recirculation valve) forcontrolling the mass air flow is finished, the second actuating element(actuator for the inlet throttle flap) immediately takes over thefurther actuating function. The end of the actuating range of anactuating element does not necessarily have to be formed by a physicalboundary. Both switchover thresholds for the active controller anddefined values for the actuating element of the deactivated controllercan be variable.

Important for switching over between the two controllers is the correctcontroller initiation, so that the controlling system (viewed from bothactuators) does not experience any unsteadiness (bumpless switching).Therefore, according to the invention, provision is made for therespective controllers to be informed of the defined values which areactually provided for the two actuating elements. These initiate thestate of the controller in accordance with the actually defined value(anti-wind-up). This is particularly advantageous, since as a result ofthe initiation with the actual defined value, said actual defined valueis used on reactivation of the previously deactivated controller as aninitial condition for controlling this actuating element, thus allowingfor the first time seamless switchover between the two controllers.

Advantages over the prior art are obtained as a result of the describedstructure with regard to the quality of the closed loop control by wayof two controllers which are optimally configured for the respectivecontrolled system, and also with regard to the flexibility provided byvariable limits for the two actuating elements, and also variabledefined values for the actuating element, the controller of which isdeactivated.

Both the quality of closed loop control and flexibility in the divisionof the actuating range are important criteria for optimising thepollutant emissions in the transient engine mode.

The two actuators are configured so as to be redundant with regard totheir influence on the mass air flow, but do not necessarily have to beidentical. The aim is the open loop control/closed loop control of twoactuating elements for the specific case that they actually areredundant if they were not bound in the actuating range or by externalinfluences. For this reason, there is no advantage to be gained bycontrolling both actuating elements simultaneously. Only the closed loopcontrol of an actuating element is active at every moment. The activecontroller passes on the closed loop control to the controller which hasjust been deactivated when it reaches the limit of its actuating range.This switchover produces a dependency between the two controllers.

As a result of the different physical marginal conditions, thetransmission behaviour of each actuator is different with respect to thecontrolled variable (for example mass air flow). There are therefore twodifferent controlled systems.

It is therefore advantageous if two different controllers are eachoptimally configured (for the time being independently of each other)for their controlled systems.

In order to reduce emissions and combustion noise, provision is made fora rapid control path, which can act and measure on each injection, totake into account the actuating behaviour of a slow control path, whichrequires in a time pattern a much longer time than the rapid controlpath, and for the repercussions on characteristic values of combustionand/or changes of at least one characteristic value of the rapid controlpath to be calculated directly from the extent of the deviation betweenthe actual values and the target values of the slow control path. Thisallows the actual combustion to be converted into a desired combustion.

In this case, a rapid control path, which can act and measure on eachinjection, takes into account a slow control path, which requires in atime pattern a much longer time.

The rapid control path is capable of collecting actual values duringeach combustion, comparing them with the target values and changing theactuating values accordingly. The slow control path is capable ofcollecting in a time pattern its measured values, comparing them withthe target values and changing the actuating values accordingly. Thetime pattern of the slow control path is much slower than the timeincrements with resolution for each combustion cycle.

The rapid control path can for example be an injection path in whichinjection parameters are calculated with resolution for each combustioncycle.

Preferably, the actual value of the slower control path is acharacteristic value of the filling of the cylinders and can be formedon the basis of a sensor-supported physical model of the inert gas ratein the cylinder prior to combustion.

The repercussions on the combustion position and/or changes of at leastone injection parameter can in this case be calculated directly from theextent of the deviation between the actual value and the target value ofthe filling of the cylinders. With the knowledge of the influence of thefilling on the combustion position, a deviation between the actualfilling and the desired filling can thus be applied directly for theclosed loop control of combustion. The influence of a deviation betweenthe actual filling and desired filling on the combustion position canthus be compensated for dynamically.

The target value for combustion can be established as in the past bydetermining the combustion position at which 50% of the fuel is burnt(MFB 50). Furthermore, the actual value of the combustion position canbe influenced by adjusting the moment of injection. In addition, theinert gas rate (inert gas mass in relation to the total mass) in thecylinder can be determined prior to each combustion event using aphysical model, based on sensor values provided. The degree of the inertgas rate takes into account both the charging pressure and the exhaustgas recirculation rate (EGR rate) and thus the influence of the chargingsystem and EGR or throttle flap actuator. As, at the fixed injectionparameters, the combustion position (MFB 50) changes in the top deadcentre region linearly with the inert gas rate characteristic variable,the repercussions on the combustion position can be calculated directlyfrom a deviation between the actual and desired inert gas rate.

The method according to the invention allows the dynamic behaviour ofthe closed loop control of combustion to be improved and thus thecomplexity of the datafication with regard to the optimisation oftransient emissions, noise, driving behaviour and driving comfort ortorque behaviour to be significantly reduced.

With the aid of sensors for air mass, temperatures and pressures, it ispossible to determine using simple physical calculations that fillingparameter which has a direct influence on combustion. By identifying acharacteristic variable of this type, it is possible to evaluate thedeviation of the current filling from the desired filling and thus topredict what repercussions this deviation will have on combustion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter in greater detail withreference to the figures, in which:

FIG. 1 is a schematic view of a device for carrying out the method;

FIG. 2 is a block diagram illustrating the method according to theinvention; and

FIG. 3 is a further block diagram for describing the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic view of an internal combustion engine 30 with afresh air tract 31, an inlet tract 34, outlet tract 32 and an exhaustgas recirculation tract 33, there being arranged in the exhaust gasrecirculation tract 33 a first actuating element 14 actuating an exhaustgas recirculation valve 10 and in the fresh air tract 31 a secondactuating element 24 actuating a throttle flap 20. Each actuatingelement 14, 24 has associated with it its own controller 1, 2. Alsoprovided is a logic 4 which decides which of the two other controllers1, 2 is activated or deactivated at each moment.

A target value for the mass air flow MAF_(ref) is determined. The targetvalue for the mass air flow MAF_(ref) and the measured actual value ofthe air mass system MAF_(meas) are used as input variables forcalculating the control deviation in the controller 1 for the exhaustgas recirculation valve 10 and the controller 2 for the throttle flap20.

A strategic function implied by the logic 4 decides which of the twocontrollers 1, 2 is activated and sets the target value for theactuating element, the controller output of which is deactivated, to apredefined value which is generated in the functions 13, 23 in which itactuates the switches 12, 22. The values for the actual defined values11, 21 of the actuating elements 14, 24 serve as input variables 11′,21′ for the corresponding controllers 1, 2. This information isnecessary for the deactivated controller to track its internal stateaccordingly and thus to allow seamless switchover between bothcontrollers.

The logic 4 operates as follows: Each actuating element 14, 24 is boundby hardware and in addition by software. For the time being, the firstactuating element 14 (actuating element for the exhaust gasrecirculation valve 10) is used to control the mass air flow MAF.Nevertheless, if the maximum opening of the first actuating element 14is reached, the second actuating element 24 takes over the furthercontrol, the first actuating element 14 being controlled via apredefined value 13 (for example the maximum opening position) (as aresult of which the controller 1 of the first actuating element 14 isdeactivated). The actuating range of the two actuating elements 14, 24is directly adjoining. The term “the maximum opening of an actuatingelement” refers to a variable limit which can flexibly be datafied andcorresponds at most to the largest mechanical opening angle of theactuator.

The two controllers 1, 2 are each optimally configured for theirstretch. This allows very high control quality to be achieved.

The logic 4 switches over between the two controllers 1, 2, wherein atall times only one of the two controllers 1, 2 is active and theactuating element of the other (deactivated) controller can be guidedbased on a defined value. The defined values for controlling theactuating element of the controller which as just been deactivated aregenerated in the functions 13, 23. The defined values are generallyvariable, although they can in specific cases correspond for example tothe boundary of the respective actuating element. Reference numeral 13denotes the function which generates the defined value for the firstactuating element 1 and 23 denotes the function which generates thedefined value for the second actuating element 2.

The stationary target value V_(S) for combustion is datafied over thecourse of the calibration process. In this case, the target value V_(S)for the reference variable is datafied at an operating point. Thistarget value must be seen in conjunction with all other operating statesat this operating point (in particular the filling). The stationarytarget value F_(S) for the filling is at the same time datafied with thetarget value V_(S) for combustion; in this case, the actuators whichdetermine the filling are set in such a way that the best possible stateis established. Based on the target value for combustion V_(S) and thefeedback about the actual combustion V_(I) on the basis of the cylinderpressure sensors, the set parameters for combustion are changed in sucha way that the actual combustion V_(I) approximates the desiredcombustion V_(S). The adjustment variables are typically fuel pathvariables: injection parameters 5 such as the moment of injection,injection pressure, quantity injected, or the like. These can beadjusted (as a function of the injection system) at least in acombustion cycle.

At the transition from one operating point to another, it is possiblefor the combustion control means 102 to set for the internal combustionengine 101 the new target value V_(S), F_(S) for the adjustmentvariables in a very short time. Nevertheless, the filling of thecylinders has very different time constants, and this leads to theadjustment values for combustion briefly not matching the currentfilling. This leads to increased emissions, increased combustion noiseand drawbacks in driving comfort or torque behaviour. To date, it hasbeen possible to reduce these influences only at very great expense.Thus; the previous system did allow combustion to be controlled in astationary manner, i.e. at an operating point with a specific filling ofthe cylinders, in such a way that the actual combustion and the desiredcombustion correspond. Deviations in the filling are compensated for bya controller in the fuel path until the actual filling F_(I) and thedesired filling F_(S) correspond. Nevertheless, rapid dynamic closedloop control of combustion was previously problematic.

These drawbacks can be reduced if the influence of the deviation in thefilling is taken directly into account in the control of combustion.With the aid of sensors 103 (air mass, temperatures and pressures), itis possible to determine, using simple physical calculations 104, theparameters of the filling that have a direct influence on combustion.Furthermore, by identifying such a characteristic variable, it ispossible to calculate the deviation of the current filling F_(I) fromthe desired filling F_(S) and thus to predict what repercussions thisdeviation will have on combustion. Suitable calculation of the fillingis a prerequisite for this.

The information about the filling deviation and the knowledge how thisdeviation affects combustion allow the influence of the deviation in thefilling to be taken directly into account in the closed loop control ofcombustion (influence equalisation).

The target value V_(S) for combustion can be established as in the pastby determining the combustion position at which 50% of the fuel is burnt(MFB 50). Furthermore, the actual value of the combustion position V_(I)can be influenced by adjusting the moment of injection. In addition, theinert gas rate (inert gas mass in relation to the total mass) in thecylinder can be determined prior to each combustion event using aphysical model 104, based on sensor values provided of standard sensors103. The degree of the inert gas rate takes into account both thecharging pressure and the EGR rate and thus the influence of thecharging system and EGR or throttle flap actuator. As, at the fixedinjection parameters, the combustion position (MFB 50) changes in thetop dead centre region linearly with the inert gas rate characteristicvariable, the repercussions on the combustion position can be calculateddirectly from a deviation between the actual and desired inert gas rate.

The method according to the invention allows the dynamic behaviour ofthe closed loop control of combustion to be improved and thus thecomplexity of the datafication with regard to the optimisation oftransient emissions, noise, driving behaviour and driving comfort ortorque behaviour to be significantly reduced.

1. A method for closed loop control of characteristic values ofcombustion in an internal combustion engine with at least one controlpath, wherein a rapid control path, which can act and measure on eachinjection, takes into account an actuating behaviour of a slow controlpath, which in a time pattern requires a much longer time than a rapidcontrol path, and wherein repercussions on characteristic values ofcombustion and/or changes of at least one characteristic value of therapid control path are calculated directly from an extent of deviationbetween actual values and target values of the slow control path.
 2. Themethod according to claim 1, wherein at least one actual value for therapid control path is determined with resolution for each combustioncycle.
 3. The method according to claim 2, wherein at least one actualvalue for the rapid control path is determined from a cylinder pressurecurve.
 4. The method according to claim 3, wherein the characteristicvalues for controlling the rapid control path are determined from atleast one actual value for the rapid control path.
 5. The methodaccording to claim 2, wherein at least one actual value for the rapidcontrol path is determined from an ion beam measurement.
 6. The methodaccording to claim 2, wherein at least one actual value for the rapidcontrol path is determined from an acceleration measurement.
 7. Themethod according to claim 1, wherein an actual value of combustion isdetermined by determining the combustion position in which 50% of thefuel is burnt.
 8. The method according to claim 1, wherein the actuatingvalue of the rapid control path can be adjusted in each combustioncycle.
 9. The method according to claim 8, wherein the actuating valueof the rapid control path is at least one injection parameter.
 10. Themethod according to claim 1, wherein the actual value of the slowcontrol path is a characteristic value of the filling of the cylinders.11. The method according to claim 10, wherein the actual value of theslow control path is the inert gas rate in the cylinder prior tocombustion.
 12. The method according to claim 11, wherein the inert gasrate in the cylinder is determined prior to combustion.
 13. The methodaccording to claim 12, wherein a physical model based on standardsensors.
 14. The method according to claim 13, wherein the repercussionson the actual values of the rapid control path and/or changes of thecharacteristic values of the rapid control path are calculated directlyfrom the extent of the deviation between the actual values and thetarget values of the filling of the cylinders.